Synchronous color conversion system

ABSTRACT

Filters are coupled to receive an uncorrected composite color television signal, which signal has been subjected to recording and reproducing operations and processed to have incoherent luminance and chrominance components, with the chrominance component color corrected. The filters separate the composite signal into its luminance and chrominance components. The chrominance component is coupled to a decoder to prepare it for subsequent encoding relative to a chrominance subcarrier reference signal that is coherent with the luminance component. The chrominance subcarrier reference signal is provided by a generator that is frequency and phase adjusted relative to the luminance component. A following encoder receives the decoded chrominance component and reference signal. The encoder responsively operates to provide a newly encoded chrominance component stabilized to the reference signal. This causes the newly encoded chrominance component to be coherent with the luminance component. Both components are then combined and coupled to a conventional line-to-line time-base corrector for correcting any time-base errors that are present in the combined components.

BACKGROUND OF THE INVENTION

Cross-reference is made to a copending U.S. Patent Application Ser. No.484,185 by Peter W. Jensen and Richard W. Palthe filed on June 28, 1974concurrently with the present application and entitled "System ForProcessing A Composite Color Television Signal Obtained From A RecordingMedium".

This invention concerns systems for eliminating timing errors from colortelevision signals and particularly from color television signals havingincoherent components.

Television signals are composite signals carrying monochrome and colorinformation and synchronizing waveforms. The synchronizing waveformsrepeat at known periodic intervals and include horizontal line pulses,vertical field pulses and color burst. The monochrome information isobtained in a luminance component and the color information in achrominance component. When the synchronizing waveforms exhibit phase orfrequency deviations with respect to a stable reference signal of thesame type, the difference in timing between these signals is a so-calledtime-base error. If time-base errors exist, distortion of the televisionpicture follows. Time-base errors are formed in systems for reproductionof composite television signals recorded on a storage medium, such asmagnetic tape. These errors are inherent to the process of translatingthe signals onto and off the tape.

Many prior art devices have been developed which deal with thecorrection of time-base errors in reproduction of television signals.

A large group of prior art color television signal reproducing systemphase-locks the chrominance signal to a stable reference subcarrierwithout fully correcting the timing errors of the composite colortelevision signal. The output signal of these reproducing systems isstabilized as to the color hue and saturation. But the remaining timingerrors inherent in the recording and subsequent reproducing process areunacceptable for some television signal applications.

As examples of the above-type prior art video recorders, the followingsystems may be mentioned: INSTAVIDEO video tape recorder (VTR)manufactured by AMPEX Corporation assignor of the present application,SONY VO-1600 VTR, SONY AV-8400 VTR. These systems employ the heterodynesignal processing technique, such as standardized by the Video TapeRecording Committee of the Electronic Industries Association of Japan(EIAJ).

For convenience, throughout the specification it will be referred to theabove type prior art video tape recorders as "EIAJ type" recorders.

For better understanding of the invention, a brief description of anINSTAVIDEO recording and reproduce system, representing a prior artEIAJ-type video tape recorder/reproduce system follows.

In the recording part of an INSTAVIDEO VTR the transmitted compositecolor television signal is separated and formed into afrequency-modulated (fm) luminance component and frequency-transposed orconverted chrominance component and then both components are combinedand recorded.

In the reproduce part of the INSTAVIDEO VTR, the chrominance component,which contains the color information and the color burst synchronizingwaveform, is separated from the luminance component by filters. Then,the original transmission frequency of both components is reconstitutedfor reproduction. At the frequency-reconstitution, a stable frequencychrominance subcarrier reference signal is utilized to correct thechrominance component in the following manner. First, the separatedchrominance component is frequency-converted to a standard 3.58 MHznominal carrier frequency. The color burst is extracted from theseparated and frequency-converted chrominance component and it isphase-compared in a phase detector with the stable frequency referencesignal from a crystal oscillator set at 3.58 MHz. The resulting phaseerror-voltage, which is representative of color errors, is employed tocontrol a voltage-controlled variable frequency oscillator whose outputfrequency variations are responsive to the detected phase error. Theoutput signal of the voltage-controlled oscillator is thenfrequency-converted to a higher frequency band. This high-band signal isin turn utilized for the above-mentioned frequency conversion of theseparated chrominance component to the standard 3.58 MHz nominal carrierfrequency. The detection of phase errors and concomitant phaseadjustment of the voltage-controlled oscillator affect elimination ofphase deviations of the color burst and, consequently, of thechrominance signal subcarrier with respect to the stable referencesignal. This results in the frequency reconstitution of a colorcorrected chrominance component.

The fm luminance component of the composite television signal, which hasbeen separated from the chrominance component in the reproduce part ofthe VTR, is first frequency demodulated to obtain its originaltransmission frequency band and then delayed to compensate the delay ofthe chrominance component due to the color-correction process. Theuncorrected and delayed luminance component is then recombined with thecolor-corrected chrominance component for output.

As a result of the record and reproduce process employed in theINSTAVIDEO tape recorder/playback system, the luminance and chrominancecomponents are permitted to become and remain incoherent with respect toeach other. Thus, the recombined components often contain time-baseerrors inherent in the recording and subsequent reproduce process. Thesetiming errors change arbitrarily during one field of the reproducedtelevision picture in either direction.

Analogously to the INSTAVIDEO, other prior art EIAJ-type tape recordersystems exhibit similar time-base errors. Applications in which highquality reproduction of the television signal is required need time-basecorrection of both chrominance and luminance component. Commonly, suchcorrection is done by conventional time-base correctors (TBC), whichperform line-to-line correction of the reproduced signal.

U.S. Pat. No. 3,763,317, assigned to the assignor of the present patentapplication, describes a TBC representative of existing conventionalsystems performing time-base corrections of composite color televisionsignals. Such time-base correctors perform line-to-line corrections ofthe recorded television signal by repositioning in time each horizontalline, consequently, each component of the television signal, such as thecolor burst, the video information, etc. The corrections are maderelative to line reference sync pulses and a chrominance subcarrierreference signal developed by independent reference sources. This isachieved by a delay device including a plurality of delay lines havebinary ordered delay periods which are selectively combined to form acomposite delay for each successive cycle of the repetitive signal. Thecombination of delay lines is selected according to comparisons of theline sync pulse and color burst of the line being corrected with thecorresponding reference signals provided by the reference sources sothat each line of signal information is synchronized with a linereference sync pulse.

Such time-base corrections assume coherency of the signal's horizontalsync and color burst components. It would be desirable to interface anEIAJ type color video recorder with a conventional line-to-linetime-base corrector of the above-described type to achieve an improvedquality of the reproduced signal from the EIAJ type recorder.

However, the output signal from these recorders is not suitable forcorrection by the TBC system for the following reasons:

The variable delay device of the time-base corrector is designed todevelop a time delay corresponding to phase deviations of the compositetelevision signal's color burst component ranging from 0° to 360°. Ifthe deviations of successive lines of the signal pass through 0° or360°, the delay provided by the delay device is advanced or retardedone-full cycle of the subcarrier, depending on the direction in whichthe deviations of successive lines change. When the passage through 0°or 360° results from the lack of coherence between the luminance andchrominance components, it causes the video signal component passingthrough the delay device to jump a time corresponding to one cycle ofthe color burst in the corresponding direction. As a result, jitter onthe television screen appears whenever the phase deviation passesthrough 0° or 360°.

From the above description it follows that the deficiencies of theprior-art EIAJ type color television recorders cannot be overcome byinterfacing them with existing line-to-line time-base correctors inorder to achieve high quality signal reproduction. Instead, when thesetwo systems are interfaced, additional timing errors of the video signalcomponent in the form of jitter are introduced.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to process acomposite color television signal obtained from a storage medium andhaving at least one component which is stabilized to a reference signalprior to line-to-line time-base correction of the composite televisionsignal.

It is another object of the invention to process a reproduced compositecolor television signal so that said composite signal is adjusted topermit interfacing of said system with a conventional line-to-linetime-base corrector.

Still another object of the present invention is to correct phase errorsof a reproduced color television signal having a stabilized chrominancecomponent which is incoherent with an uncorrected luminance component byphase-locking the stabilized chrominance component to the uncorrectedluminance component.

Still a further object of the invention is to produce a stabilizedchrominance component which is coherent with an uncorrected luminancecomponent, which components form a composite color television signal.

Still another object of the invention is to process an output signal ofan EIAJ-type video recorder to render it suitable for line-to-linetime-base correction.

The above presented and further objects of the invention areaccomplished by a system for processing a composite color televisionsignal reproduced from a storage medium which reproduced signal has astabilized chrominance component that is incoherent with its luminancecomponent and vertical field, horizontal line, and color burstsynchronizing components. In the system, means for separating thestabilized chrominance from the luminance component are utilized. Adecoder receives the stabilized chrominance component and prepares itfor subsequent encoding relative to a first reference signal that iscoherent with the luminance component. To prepare the chrominancecomponent for such subsequent encoding, the decoder frequency convertsthe chrominance component relative to a second reference signal having aknown nominal frequency. The decoded chrominance component is coupled toa following encoder. The following encoder also receives the firstreference signal and responsively operates to frequency convert thechrominance component relative to the first reference signal and,thereby, provide a newly encoded chrominance component stabilized to thereference signal whereby it is caused to be coherent with the luminancecomponent.

Other objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments and accompanying drawings, wherein:

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a block diagram of a reproduce system of a heterodyne videotape recorder in accordance with the invention claimed in thecross-referenced patent application.

FIG. 2 is a block diagram of a sync coherent subcarrier generatorutilized in the present invention.

FIG. 3 is a block diagram of a reproduce system of a heterodyne videotape recorder arranged to provide coherent chrominance and luminancecomponents directly from the signals obtained from the video tape inaccordance with the invention claimed in the cross-referenced patentapplication.

FIG. 4 is a block diagram of a synchronous color conversion system, inaccordance with the present invention.

FIG. 5 is a block diagram of another embodiment of a synchronous colorconversion system, in accordance with the present invention.

FIG. 6 is a block diagram showing connection of the synchronous colorconversion system in accordance with the present invention to a VTR andTBC, respectively.

FIG. 1 represents a reproduce system of a heterodyne VTR in accordancewith the invention claimed in the cross-referenced patent application. Acomposite color television signal is received from the tape and appliedvia an input terminal 8 to a high pass filter 9 of 2.7 MHz in parallelwith a band pass filter 14 of 767 kHz. The output signal of the highpass filter 9 is the separated frequency modulated luminance component.The luminance component is then decoded or demodulated by a frequencydemodulator 11 to frequency convert it to its original transmissionfrequency and the demodulated signal is passed through a delay line 12,which provides a time delay for matching the delay of the chrominancecomponent due to its processing. The output signal of the band passfilter 14 is the separated chrominance component, containing the colorinformation and color burst. This chrominance component is decoded orfrequency-converted (heterodyned) by a first frequency converter 15 toits nominal carrier frequency of 3.58 MHz at which it was transmittedprior to the recording. In accordance with the embodiments of FIGS. 1and 3, the signal utilized for heterodyning is a control signal whichrenders the output signal of the converter 15 to be coherent with theabove-mentioned luminance component, which process will be describedlater. The delayed luminance component at the output of the delay line12 is then combined with the coherent chrominance component and thecombined signal is thus suitable for time-base error correction in aconventional line-to-line time-base corrector (TBC).

Now the embodiment of FIG. 1 will be described in more detail.

The burst signal is extracted from the frequency converted chrominancesignal by connecting the input of a burst gate 20 in the path of saidchrominance component. Burst gate 20 is controlled by a sync separator31 which has its input connected in the path of the demodulatedluminance signal. Sync separator 31 extracts horizontal sync pulses fromthe demodulated luminance signal and causes the generation of burst gatepulses. These burst gate pulses in turn control gate 20 so that thelatter is open only during the duration of each burst signal.

A sync coherent chrominance subcarrier generator 10 is provided, whichproduces an output signal of 3.58 MHz, coherent with the luminancecomponent. Its block diagram is shown in FIG. 2 and will be describedlater.

A phase detector 21 measures the phase difference between thechrominance subcarrier at the output of filter 17, which signal isrepresented by the color burst, and the sync coherent subcarrier at theoutput of generator 10. Since the output signal of generator 10 containsthe phase deviations of the luminance component, the error signal at theoutput of the phase detector 21 is responsive to these phase deviations.The output of the phase detector 21 is connected to an input of avariable-frequency oscillator, which is implemented by avoltage-controlled oscillator 22. The nominal frequency of thisoscillator is set at 767 KHz and it is controlled by the above-describederror signal. The output signal of the oscillator 22 is fed into aninput of a second frequency converter, which is implemented by abalanced modulator 23. The other input of modulator 23 is connected tothe output of generator 10. Balanced modulator 23 converts the outputfrequency of oscillator 22 to a higher frequency band of 4.34 MHz. Thesum frequency of 3.58 MHz and 767 kHz at the output of the balancedmodulator 23 is filtered by a band-pass filter 24 of 4.347 MHz andapplied to one input of the balanced modulator 15. The signal at theoutput of the second balanced modulator 23 serves as a control signalutilized by the first balanced modulator 15 for the subsequent frequencyconversion of the chrominance component. This control signal is derivedfrom the coherent subcarrier signal, in the above disclosed manner bywhich a chrominance subcarrier at the output of the modulator 15 isobtained, which is coherent with the luminance component.

The other input of modulator 15 is connected to the output of thepreviously mentioned band-pass filter 14. The difference frequency atthe output of the balanced modulator 15 is passed through a band-passfilter 17 of 3.58 MHz. The coherent chrominance and luminance componentsare then combined in a signal adder 13 and fed into an output terminal25. The resulting output signal is suitable to be fed into aconventional line-to-line time-base corrector.

As an alternative to the preferred embodiment of the invention, shown inFIG. 1, the frequency conversion of the separated chrominance componentto 3.58 MHz nominal carrier frequency could be performed in one step,utilizing only one balanced modulator 15 and omitting modulator 23.(This alternative embodiment is not shown). This could be achieved, ifthe oscillator 22 would have a nominal frequency of 4.347 MHz. It isobvious that a signal of this frequency could be used as a controlsignal fed directly into the first balanced modulator 15.

Now the generator 10 for producing a sync coherent subcarrier signal of3.58 MHz shown in FIG. 2 will be described. The horizontal linesynchronizing pulses, which are coherent with the luminance component,are separated from the demodulated luminance signal received at theoutput of demodulator 11 by the sync separator circuit 31, as shown inFIG. 1. The separated horizontal pulses having a nominal frequency of15.734 kHz are fed from the output of the separator 31 into one input ofa phase detector 32. A variable-frequency oscillator, which isimplemented by a voltage controlled oscillator 33, having a nominalfrequency of 7.16 MHz is connected to the output of the phase detector32. The output of the oscillator 33 is fed into an other input of thephase detector 32. Thus, the phase detector 32 detects the phasedeviations of the horizontal sync pulses, received from the tape, withrespect to the output signal of the voltage-controlled oscillator 33.The frequency of the oscillator 33 is in turn controlled by the outputof the phase detector 32. Consequently, the output signal frequency ofthe oscillator varies with the detected phase-variations of thehorizontal sync pulses. The output frequency of 7.16 MHz of theoscillator is adjusted by a frequency divider 34, to be equal to thehorizontal sync pulse frequency of 15.734 kHz. Thus, the divider 34performs a division of the oscillator output frequency by 455. Anotherfrequency divider 35 is connected also to the output of the oscillator33. Frequency divider 35 divides the output signal frequency of theoscillator 33 by 2, to adjust it to the nominal frequency of 3.58 MHz ofthe color burst signal. The output signal of frequency divider 35 is async coherent signal of 3.58 MHz and thus suitable for phase-detectionin the phase-detector 21 with respect to the phase of the color burstsignal entering in the phase detector 21 via its other input as shown inFIG. 1.

From the above-description of the subcarrier generator 10 shown in FIG.2 follows, that the generator 10 produces an output signal of 3.58 MHzwhich is phase-locked to, and thus coherent with the luminance signalcomponent.

In the previous description of a prior-art INSTAVIDEO reproduce systemit was mentioned that a stable crystal reference oscillator of 3.58 MHzis utilized to produce a reference signal which is then phase-comparedwith the color burst and the resulting phase-deviation is utilized tocorrect the color component. Such a stable crystal oscillator 26 isshown in FIG. 1. A switch 18 is provided. To its pole, phase detector 21and balanced modulator 23 are connected permanently, while by itscontacts the sync coherent subcarrier generator 10 is connectedalternately with the stable crystal generator 26, depending on theinstant position of switch 18. This provision makes possible tointerconnect generator 10 into a prior art reproduce system and toselect the desired type of generator, depending on whether thereproduced signal will be further processed by a line-to-line TBC.

FIG. 3 shows another preferred embodiment of the invention claimed inthe cross-referenced patent application. It is a reproduce system inwhich a composite color television signal is received from the tape atan input terminal 40 and is thereafter separated into chrominance andluminance components. The luminance component passes through a high-passfilter 41 and is subsequently decoded or demodulated by a frequencydemodulator 42. To the output of the demodulator a delay line 43 iscoupled to match the delay of the chrominance component due to itsprocessing. The output of the delay line 43 is fed into one input of asignal adder 44.

A band-pass filter 45 separates the chrominance component from theluminance. The separated chrominance component is frequency-converted ina balanced modulator 46 to a higher frequency band, corresponding to theconventional transmission frequency of the chrominance signal set at3.58 MHz. The second input signal of the modulator 46 utilized for thefrequency conversion of a control signal that causes the output signalof the balanced modulator 46 to be coherent with the line synchronizingpulses, as will be explained later.

The circuit for producing this control signal will now be described.

The separated chrominance signal at the output of the band-pass filter45 is frequency converted by a first balanced modulator 47 to a higherfrequency band at a carrier frequency of 4.27 MHz, which is the sum ofthe off-tape chrominance signal nominal carrier frequency 688 kHz and ofa nominal 3.58 MHz signal. The signal of 3.58 MHz is supplied by a synccoherent subcarrier generator 10 which is of the same type as previouslydisclosed and shown in FIG. 2. It has been previously described indetail, that the output of the generator 10 is a subcarrier signalcoherent with the luminance component of the composite television signalreceived from the tape. The output signal of the modulator 47 passesthrough a 4.27 MHz band pass filter 48. Thus the output signal of thefilter 48 is the sum of the unstable 688 kHz chrominance carrier and ofthe sync coherent 3.58 MHz signal supplied by the generator 10. Theoutput of the filter 48 is coupled to the input of a burst gate 49. Theburst gate 49 is controlled by the output of a sync separator 50. Theburst gate 49 extracts the burst signal from the chrominance signal atthe output of band pass filter 48 only during the burst intervals. Aphase detector 51 is employed to phase-compare the output signal of theburst gate 49 with the above-mentioned control signal at the input ofmodulator 46. This control signal is supplied by a color correctioncircuit comprising elements 51, 52, 53, 54 and 55. The output signal ofthis color correction circuit is frequency and phase-related to theburst signal at the output of the band-pass filter 48 and has nosignificant phase variations with respect to said burst signal. Theinstabilities of the two input signals of the balanced modulator 46 areof complimentary character and are canceled in the subsequent conversionprocess. The resulting output signal of modulator 46 is a sync coherentchrominance signal having a nominal carrier frequency of 3.58 MHz.

Now the circuit for color correction of the chrominance component willbe described. A voltage-controlled oscillator 52 is coupled to theoutput of phase detector 51. The nominal frequency of the oscillator is688 kHz. The output of oscillator 52 is coupled to one input of a secondbalanced modulator 53. To the other input of modulator 53 the output ofa 3.58 MHz reference crystal oscillator 55 is coupled. The sum-frequency4.27 MHz of the output signal of the balanced modulator 53 is passedthrough a band-pass filter 54 and the output signal of filter 54 is fedback to the other input of the phase-detector 51. The phase detector 51detects the phase differences between the filtered burst signal at theoutput of the burst gate 49 and control signal at the output of filter54. The gain from the feedback loop comprising the phase comparator 51,oscillators 52 and 55, modulator 53 and filter 54 is such that theoutput signal of the filter 54 has no significant phase variations withrespect to the burst signal at the output of burst gate 49. The outputof filter 54 is coupled to the other input of the balanced modulator 46,to the first input of which the off-tape uncorrected chrominancecomponent from the band-pass filter 45 is fed. The difference frequencyof both input signals of this balanced modulator 46, which is thenominal 3.58 MHz carrier frequency, is fed through a band-pass filter 57to the other input of the signal adder 44. The coherent chrominance andluminance signal components are combined in the signal adder 44. Theoutput signal of the signal adder at terminal 56 is thus made suitablefor processing by a line-to-line time-base corrector. Thus, the signalreproduce system of the preferred embodiment of the invention shown inFIG. 3 may be readily interfaced with a conventional TBC, to eliminatethe time-base errors of both the chrominance and luminance signalcomponents inherent to the recording and subsequent reproducing process.

In an alternative embodiment of the system shown in FIG. 3, instead ofthe stable reference oscillator 55 a sync coherent subcarrier generator10 may be employed. This modification of the system is not necessary toachieve the phase-locking of the chrominance component to the luminance,but may be of advantage to the system. Instead of using two differentoscillator circuits 10 and 55, just one circuit 10 providing two outputsmay be sufficient for the entire system. Another advantage of thismodification is that the above-disclosed color-correction feedbackcircuit would operate with considerably smaller error signals, if bothrference signal generators 10 and 55 would be implemented by one singlegenerator with two outputs.

Analogously to the previously described embodiment shown in FIG. 1, aswitch (not shown) similar to switch 18 may be utilized in theabove-described system of FIG. 3. Such a switch would selectively andalternatively interconnect generator 10 or a stable crystal oscillatorsuch as oscillator 55, respectively, with the reproduce system dependingon whether a further line-to-line time-base error correction isrequired.

The embodiments described hereinabove with reference to FIGS. 1-3 arerepresentative of implementations of the invention subject of myabove-identified cross-referenced application. Embodiments of theinvention subject of this application are shown in FIGS. 4 and 5,respectively. The generator shown in FIG. 2 is utilized in therespective embodiments of the present invention as well as that of thecross-referenced application.

The embodiment of the present invention shown in FIG. 4 will now bedescribed in detail.

In this system for processing a composite television signal reproducedfrom a storage medium, an output signal from an EIAJ-type video taperecorder is received at an input terminal 60. In the previousdescription of the prior art EIAJ-type video tape recorders, it has beenexplained and emphasized that the output signal of an EIAJ-type VTR isnormally color corrected with respect to an independent stable referencesignal, but the time-base errors of the chrominance and luminancecomponent stay uncorrected. As a result, chrominance and luminancecomponents at the output of an EIAJ-type video recorder are incoherentand unsuitable for correction in conventional time-base correctors.

The signal received at the input terminal 60 consists of an uncorrectedcomposite color television signal, including a frequency-demodulatedluminance component and a frequency-converted chrominance component, thelatter component having a nominal carrier frequency of 3.58 MHz andcontaining the color information and color-burst. The luminancecomponent is separated from the chrominance component by a low-passfilter 61 of 2.2 MHz which is followed by a delay line 62. Thechrominance component, which is incoherent with the luminance component,is passed through a band-pass filter 63 of 3.58 MHz, to eliminate thelow-frequency components. The separated chrominance signal is thendecoded or frequency-converted in a first frequency-converter 64 to alower carrier frequency to prepare it for subsequent encoding relativeto a reference that is coherent with the luminance component. The firstfrequency converter 64 comprises a first balanced modulator 65 to oneinput of which a stable crystal oscillator 66 is coupled to providethereto a signal at a known nominal frequency of 4.347 MHz. To the otherinput of the first balanced modulator the output of the first band-passfilter 63 is coupled. The difference frequency at the output of thefirst balanced modulator 65, which has a nominal carrier frequency of767 kHz, is passed through a second band-pass filter 67, whicheliminates the unwanted frequency components. The output signal of thefirst frequency converter 64 which is at the same time the output signalof the second band-pass filter 67 is then fed into an encoder or secondfrequency-converter 68, which converts the chrominance signal back toits nominal carrier frequency of 3.58 MHz. Analogously with the firstfrequency converter, the second frequency converter 68 comprises asecond balanced modulator 69 followed by a third band-pass filter 70.

A voltage-controlled oscillator 71 is coupled to one input of the secondbalanced modulator 69, and supplies a reference control signal derivedfrom the coherent subcarrier signal. The generation of this controlsignal will be described now.

Analogously to the previously described embodiments, a sync coherentsubcarrier generator 10, similar to that shown in FIG. 2, is utilized.The input signal of this generator 10 is the output signal of a syncseparator 72, which extracts the horizontal line sync pulses from theincoming composite signal. The output signal of said sync coherentgenerator 10 is fed into one input of a phase comparator 73. The colorburst signal is extracted from the chrominance component at the outputof the second frequency converter 68 by a burst gate 74. The burst gate74 is controlled by burst gate pulses derived by the sync separator 72.The extracted burst signal at the output of the burst gate 74 is fedinto the other input of the phase-comparator 73. The phase detector 73compares the phase of the reproduced color burst with the phase of theoutput signal from generator 10, and develops an error signal responsiveto the resulting phase deviation. The error signal at the output of thephase detector 73 is utilized to control the frequency of thevoltage-controlled oscillator 71. As it has been above mentioned, theoutput of the voltage-controlled oscillator is coupled to one input ofthe second balanced modulator 69. The nominal frequency of thevoltage-controlled oscillator is set at 4.34 MHz, which frequencydeviates corresponding to the deviations of the error voltage at theoutput of the phase-detector 73. The output signal from the oscillator71 is the above-mentioned control signal. It is mixed with thefrequency-converted chrominance component in the second balancedmodulator 69 and the resulting difference-frequency signal at the outputof the second balanced modulator 69, which has a nominal carrierfrequency of 3.58 MHz, is filtered in the band-pass filter 70, aspreviously described. The output signal of the second balanced modulatoris thus a frequency-reconverted chrominance component, which has beenmade coherent with the horizontal sync pulses and consequently also withthe luminance component.

The delayed luminance component and the color-corrected and coherentchrominance component are combined in a signal adder 75 and fed into anoutput terminal 76.

The output terminal 76 may be interconnected with a conventionaltime-base corrector, performing line-to-line corrections, and thus animproved reproduction of a recorded color television signal may beachieved. FIG. 6 shows the input of a synchronous color correctionsystem 101 in accordance with the present invention, connected toreproduce signal output of a conventional VTR 100, which supplies areproduced color television signal having incoherent luminance andchrominance components. The output of the system 101 is connected to anuncorrected signal input of a conventional TBC 102 for providingline-to-line time base correction of television signals obtained fromsystem 101. It should be noted with respect to the above-describedembodiment of the invention shown in FIG. 4 that the specificfrequencies related to the block diagram have been chosen only asexamples to facilitate the understanding of the invention. Othersuitable frequencies may be selected as well for proper operationwithout departing from the scope of the invention.

Thus, known nominal frequency of the nominal stable oscillator 66 has tobe greater or less than the color subcarrier frequency by an amountwhich will produce a suitable sum or difference frequency at the outputof the balanced modulator 65. This oscillator frequency must be highenough to accomodate the color sidebands without fold-over and should beeasy to separate from the other components. Consequently, the centerfrequency of the band-pass filter 67 is chosen to be equal to thedesired sum or difference frequency component of the modulator 65 outputand the bandwidth of the filter should be sufficient to pass the colorsidebands. The frequency of the voltage controlled oscillator 71 ischosen so that either the sum or the difference nominal frequencycomponent in the output signal of the balanced modulator 69 is the sameas the original nominal subcarrier frequency. The desired output signalcomponent is then selected by the band-pass filter 70 with adequatebandwidth to pass the color sidebands.

Finally, FIG. 5 shows a preferred embodiment of the invention, which isstill different in details from that previously described and shown inFIG. 4. The embodiment shown in FIG. 5 receives an output signal from anEIAJ-type video recorder, at an input terminal 80. The luminancecomponent of the received signal is separated from the chrominancecomponent by a low pass filter 81. The filter 81 is followed by adelay-line 82 to match the delay of the chrominance component resultingfrom its processing.

A band-pass filter 83 of 3.58 MHz separates the chrominance componentfrom the luminance.

In the embodiment of FIG. 5, the adjustment of the chrominance componentto render it coherent with the luminance component is performed in twobasic steps which steps may be designated as frequency-decompositiondecoding of the chrominance signal to remove the color information fromthe high frequency carrier signal, followed by its subsequentfrequency-reconstitution encoding by placing the color information on acarrier signal. In the embodiment of FIG. 4, frequency-converting thechrominance component to a lower carrier frequency followed by asubsequent reconverting it to its original carrier frequency isemployed.

While both embodiments involve frequency conversion of the chrominancecomponent, in the embodiment of FIG. 5, the steps are performed in adifferent way. The frequency-decomposition of the chrominance componentis done by a color decoder 84, which decodes the component into itscolor signal components I and Q or color difference signals B-Y and R-Y.The color decoding is done by demodulation of the chrominance component,which is a process well known in the art. Color decoding of thechrominance component is done with respect to the extracted color burstsignal, which has a known nominal frequency. The extracted color burstis made continuous in the following manner. The color burst signal isextracted from the separated chrominance signal at the output of thefilter 83 by a burst gate 85. Burst gate 85 is controlled by a syncseparator 86 in a similar way as previously described with reference toother embodiments. The output signal of the burst gate 85 is fed intoone input of a phase detector 87. A voltage-controlled crystaloscillator 88 is coupled to the other input of the phase-detector 87.The nominal frequency of the oscillator 88 is 3.58 MHz. The phase of theincoming color burst signal from the output signal of said EIAJ-typevideo recorder is compared to the phase of the output signal ofoscillator 88 in the phase comparator 87 and the resulting error voltageis fed back to the input of the voltage-controlled oscillator 88. Theoutput signal of the oscillator 88 is thus voltage-controlled toeliminate the phase errors of the incoming burst signal with respect tothe reference signal from the oscillator 88. The output signal of theoscillator 88 thus serves as a reference signal for the color decoding.

In the step of the color signal reconstitution, the I and Q or B-Y andR-Y components, respectively are encoded on a sync coherent subcarrier.The color signal components I and Q or B-Y and R-Y at the output of thecolor decoder 84 are fed into the input of a color encoder 89. For colorencoding, the output signal of the sync coherent subcarrier generator 10is utilized as a reference subcarrier, onto which the components I and Qor B-Y and R-Y are encoded. The encoding is performed by quadraturemodulation of the I and Q or B-Y and R-Y components respectively usingsaid reference subcarrier, which is coherent with the luminancecomponent, as has been previously described.

Thus, the output signal from the color encoder 89 is a modulatedchrominance component having a nominal carrier frequency of 3.58 MHzwhich is coherent with the luminance component. This chrominancecomponent is combined with the delayed luminance component in a signaladder 90 and fed into an output terminal 91. The output signal at theterminal 91 is thus made suitable for line-to-line time-base correctionin conventional time-base correctors.

By interfacing the input of the synchronous color conversion system ofthe preferred embodiments of the invention above-described and shown asin FIGS. 4 and 5 respectively, with an EIAJ-type video tape recorder,and by interfacing the output of that system with a conventional TBC, asshown in FIG. 6, an improved television signal is obtained, whichcomplies with the broadcast standards.

The above-described preferred embodiments of the invention are designedfor use in the NTSC color television system. However, the invention maybe adapted for use in other television systems as well.

While several embodiments of the invention have been illustrated anddescribed, it is to be understood that these were given merely for thepurpose of explanation. It will be apparent to those skilled in the artthat many modifications and variations of the invention may be effectedwithout departing from the scope of the novel concepts of the inventionas set forth in the appended claims.

What is claimed is:
 1. A system for processing a composite colortelevision signal having vertical field, horizontal line, and colorburst synchronizing components and incoherent luminance and chrominancecomponents, said luminance component being coherent with said horizontalline synchronizing component, said chrominance component being coherentwith said color burst synchronizing component, and said components beingat nominal transmission frequency bands, comprising:(a) means coupled toreceive said composite signal and separate said chrominance andluminance components; (b) means responsive to said horizontal linesynchronizing component to generate a first reference signal coherentwith said luminance component; (c) means for generating a secondreference signal at a known nominal frequency; (d) means responsive tothe color burst synchronizing component and one of said first and secondreference signals for providing a phase corrected reference signal, theother of said first and second reference signals being a phaseuncorrected reference signal; (e) decoding means coupled to receive saidseparated chrominance component for frequency decomposing it in responseto and with respect to the phase of a decoding reference signal; (f)encoding means coupled to receive said frequency decomposed chrominancecomponent for reconstituting the chrominance component at said nominaltransmission frequency in response to and with respect to the phase ofan encoding reference signal; and (g) one of said phase corrected andsaid phase uncorrected reference signals coupled to the decoding meansas the decoding reference signal and the other signal coupled to theencoding means as the encoding reference signal.
 2. A system accordingto claim 1 wherein:(a) said decoding means comprises a first frequencyconverter coupled to receive said separated chrominance component forconverting it from its nominal transmission frequency band to adifferent frequency band; (b) said encoding means comprises a secondfrequency converter coupled to receive said separated and convertedchrominance component and said encoding reference signal for convertingsaid different frequency band chrominance component to the nominaltransmission frequency band of said chrominance component; and (c) saidmeans for providing a phase corrected reference signal comprises:a burstgate coupled to said second frequency converter for extracting saidcolor burst component from its output; a phase detector coupled to saidburst gate for detecting the phase of said extracted burst componentwith respect to the phase of said first reference signal, said phasedetector produces a corresponding error voltage; and a variablefrequency oscillator means coupled to receive said error voltage forproviding said phase corrected reference signal with its frequency andphase adjusted according to said error signal to be coherent with saidfirst reference signal, said phase corrected reference signal coupled toa control input of said second frequency converter as the encodingreference signal.
 3. A system according to claim 2, wherein said meansfor generating said first reference signal coherent with said luminancecomponent comprises:(a) means for separating said horizontal linesynchronizing component from said composite television signal; (b) asecond variable frequency oscillator means providing said firstreference signal; and (c) a second phase detector for detecting thephase of said horizontal line synchronizing component with respect tothe first reference signal of said second variable frequency oscillatormeans and producing a corresponding second error signal to control thefrequency and phase of the first reference signal provided by saidsecond variable frequency oscillator means.
 4. A system according toclaim 1 wherein:(a) said decoding means comprise a color signal decodercoupled to receive the separated chrominance component and responsive tothe second reference signal as the decoding reference signal fordecoding said separated chrominance component into its color components;and (b) said means for providing a phase corrected reference signalcomprises:a burst gate for extracting said burst synchronizing componentfrom said separated chrominance component at the input of said decodingmeans; and a phase detector for comparing the phase of said extractedburst synchronizing component to that of said second reference signaland producing a corresponding error signal coupled to the means forgenerating the second reference signal to control the frequency andphase of the second reference signal to provide thereby a phasecorrected second reference signal.
 5. A system according to claim 4,wherein said encoding means comprises a color signal encoder forencoding said color components by quadrature modulation with respect tosaid coherent first reference signal.
 6. A system according to claim 1further comprising a color video reproduce system providing saidcomposite color television signal coupled to an input of said separatingmeans.
 7. A system according to claim 1 further comprising means coupledto receive and combine the reconstituted chrominance component andseparated luminance component; and a time-base corrector for performingline-to-line correction of a reproduced color television signal havingcoherent components coupled to receive the combined components.
 8. Asystem according to claim 7 further comprising a color video reproducesystem providing said composite color television signal coupled to aninput of said separating means.
 9. An apparatus for processing acomposite color television signal reproduced by a video reproducesystem, said signal having incoherent chrominance and luminancecomponents, and vertical field, horizontal line and color burstsynchronizing components, said luminance component being coherent withsaid horizontal line synchronizing component and said chrominancecomponent being coherent with said color burst synchronizing component,said components being at nominal transmission frequency bands, saidapparatus comprising in combination:(a) means for receiving saidcomposite signal from said video reproduce system; (b) means forseparating said received signal into a low frequency band luminancecomponent and into a high frequency band chrominance component, saidseparated high frequency band chrominance component containing saidcolor burst component; (c) means for generating a reference signal of aknown frequency; (d) means for frequency-converting said separated highfrequency chrominance component into a different frequency band inresponse to the reference signal of a known frequency; (e) means forgenerating a reference subcarrier signal coherent with said luminancecomponent; (f) means responsive to a control signal derived from saidreference subcarrier signal for frequency-reconverting saidfrequency-converted chrominance component to its nominal transmissionfrequency band; (g) means coupled to said frequency-reconverter meansfor extracting said burst component from said frequency-reconvertedchrominance component; (h) means for phase-comparing said extractedburst component with said reference subcarrier signal to provide saidcontrol signal; and (i) means for combining said separated luminancecomponent and said frequency-reconverted chrominance component into acomposite color television signal.
 10. An apparatus for processing acomposite color television signal reproduced by a video reproducesystem, said signal having incoherent chrominance and luminancecomponents, and vertical field, horizontal line and color burstsynchronizing components, said luminance component being coherent withsaid horizontal line synchronizing component and said chrominancecomponent being coherent with said color burst synchronizing component,said components being at nominal transmission frequency bands, saidapparatus comprising in combination:(a) means for receiving saidcomposite signal from said video reproduce system; (b) means forseparating said received signal into a low frequency band luminancecomponent and into a high frequency band chrominance component, saidseparated high frequency band chrominance component containing saidcolor burst synchronizing component; (c) means for extracting said colorburst synchronizing component from said separated high frequency bandchrominance component; (d) means for generating a reference signal; (e)means for phase-comparing said extracted color burst synchronizingcomponent with said reference signal and producing an error signalcoupled to said reference signal generating means for controlling thefrequency and phase of said reference signal; (f) means responsive tosaid reference signal for color decoding said separated chrominancecomponent into its color components; (g) means for generating anotherreference signal coherent with said luminance component; (h) meansresponsive to said other reference signal for color encoding saiddecoded color components; and (i) means for combining said luminancecomponent and said color encoded chrominance component into a compositecolor television signal.
 11. For use in a video signal processing systemfor removing time base errors from video type information signals, aninput color processor for modifying input color video signals of theprocessed color type prior to removal of time base errors therefrom,said input color processor comprising means for separating said incomingprocessed color video signals into chroma and luminance portions, meansfor converting said chroma signals into equivalent chroma signals phaselocked to a variable frequency input clock reference signal train, saidvariable frequency input clock reference signal train being coherentwith said luminance portion, means for delaying said separated luminanceportion by a period equivalent to the delay of said chroma portion ofthe corresponding line in passing through said converting means, andmeans for combining said delayed luminance portion with said phaselocked equivalent chroma signals, wherein said converting meanscomprises means including a phase lock loop for generating a colordemodulation carrier signal train derived from the burst portion ofsucceeding lines of incoming color video information, means fordemodulating the separated chroma portions into quadrature componentswith the color demodulation carrier signal train, and means forre-encoding said quadrature color components with said variablefrequency input clock reference signal train to generate chroma signalscontaining the original color information phase locked to said inputclock reference signal train.